intermittent trouble getting motors to run

[natterbus]

I am wondering if anyone is having similar difficulty because I think it must be a firmware or software issue.

We competed last December, used the robot for one project in March and had hardly touched it until a week ago. Last week we tried to run last year's table but one motor wouldn't run and the program seemed to get hung up with 1 motor spinning. After playing around a bit, we pulled out the connecting wires, plugged them back in and everything worked all of a sudden.

The issue was forgotten until today. My kids built a new robot and wrote a simple program to test it out. Again only 1 motor spun. The 2nd motor kind of jerked every once in a while. The program seemed to be hung up on the first block because it never got past the spinning motor to where it was supposed to display an image to the screen. I changed wires....same issue. I plugged the wire to the non-functioning motor into a 3rd motor that wasn't attached to the robot...same issue. I downloaded the program to our other brick and plugged the motors into that brick...same issue. I tried motor port A instead of B...same issue. I swapped the wires going into ports B and C such that motor and wire B became motor and wire C and vice versa...oddly port C which had been working stopped and port B worked instead.

All of a sudden I got it to work with our 2nd brick (different robot). Then I swapped out for out 1st brick and it didn't work the first time. Changed some wires, made sure connections were tight and voila...it started working and has worked every time since.

We downloaded the latest firmware in the middle of this...not sure if we had it already. So we have the latest. Am I correct in thinking there must be something malfunctioning with the software? or perhaps the download process I suppose? Has anyone seen this problem where only one motor spins, the other kind of jerks once in a while and the program gets hung up? It seems like just a loose connection but I checked that 15 times and reproduced it on another brick.

What on earth is going on?!! Thanks! natterbus

eta: my son used the view mode to check rotations on the "malfunctioning motor" as he spun the motor by hand. It was registering minimally on what should have been a high reading (i.e. 1 degree rather than 100)

[dnb]

Originally Posted by natterbus

my son used the view mode to check rotations on the "malfunctioning motor" as he spun the motor by hand. It was registering minimally on what should have been a high reading (i.e. 1 degree rather than 100)

Sounds like a broken rotation sensor.

Try the following: Create a program that has one motor block set to run for 1 rotation. See if the questionable motor operates as intended. If the motor keeps spinning past 1 rotation, the rotation sensor probably isn't taking correct readings, and the motor is definitely broken.

Check all your other motors with the above test.

[natterbus]

The rotation sensor is built into the motor right? Since I was able to get it to reproduce with other motors I don't think that could be the issue. Of course now I can't get it to reproduce, though 1 of the motors isn't behaving consistently on startup and it may be related. Natterbus

[dna1990]

I would go back to cables. I know you swapped those too, but agree if other motors DID show the problem - I would doubt it is the motor or its internal rotation sensor.

And the fact it has disappeared for now, tends to leave out the brick, program, firmware.

The cables (at least on our robot) get bent and kinked trying to route them around the bot. They seem a likely source when the 'intermittent' word comes up.


As I wrote this, and thinking about the time that has passed and the issue has gone into remission. Are you 'sure sure' the program wasn't changed? Is this real code, or do you have a very small and consice 'test motor' program that you know is solid?

[Dean Hystad]

Originally Posted by natterbus

The rotation sensor is built into the motor right? Since I was able to get it to reproduce with other motors I don't think that could be the issue. Of course now I can't get it to reproduce, though 1 of the motors isn't behaving consistently on startup and it may be related. Natterbus

I don't know if this could be the reason for your inconsistent starts, but I had my boys thinking I was some kind of fortune teller or robot whisperer because I could predict exactly what the robot was going to do at the start and could make the same program work or fail on demand.

http://forums.usfirst.org/showpost.p...7&postcount=35

[natterbus]

Thanks! I could believe it is a wire issue. Some of the connections just don't seem to have the "snap" they originally had. Also, the first time the issue came up, we pulled out the wire, plugged it back in and the problem went away. At the time I just assumed it wasn't plugged in all the way. But the second time it came up, we kept double checking that the connections were all the way in. The behavior was seemed very similar to failing to plug in the 2nd motor except for the slight spasms the motor would make once in a while, usually at startup.

Actually I keep having issues with my laptop charging cords flaking our on me...clearly I'm hard on wires so maybe my kids are too

We did not change the program while testing the issue. It was just a simple go forward, beep, display an image to the screen. It would never get past "forward" # of degrees, presumably because the rotation sensor continued to register zero.

Dean, While I don't think that was the issue at that particular moment, it is a good thing to keep in mind. It is possible that as we were messing around with it, possibly hand turning motors as we were testing, that we may have thrown off the rotation sensor, compounding our confusion. From what you are saying, I assume the rotation sensor auto-resets to zero every time you start a program?

Thanks for all your help! There seem to be endless quirks to learn about this system.

Natterbus

[Dean Hystad]

Originally Posted by natterbus

Dean, While I don't think that was the issue at that particular moment, it is a good thing to keep in mind. It is possible that as we were messing around with it, possibly hand turning motors as we were testing, that we may have thrown off the rotation sensor, compounding our confusion. From what you are saying, I assume the rotation sensor auto-resets to zero every time you start a program?

Everything that is relative starts at zero when you start a program. Timers, rotation sensors, the motor commands, variables (No for Yes/No and empty string for text).

[natterbus]

It happened again! This time the robot worked all day. All of a sudden it started spinning in place. Holding it in the air upside down and studying the motors, this time the right motor was actually spinning very slowly backwards as the left motor went ahead at what seemed to be the correct speed. The program merely said "go forward until touch sensor is triggered". It happened a few times despite re-downloading the program. I switched the wire going to the "bad motor" and ran the program again. It still happened! Then just as suddenly as it started, it went back to working just fine. At least this time I put an "x" on the suspect motor and I don't see how it could be a wire since I was very careful in my testing this time to keep track of what I was doing. Can't do further tests until it stops working again! But I think I am going to switch out that motor, put it aside, and hope this never crops up again!

Natterbus

[Linda Zoe]

The last week of school in June, I built 6 identical simple robots (except each had tires with different diameters) and taught all my 5th grade students (75 total from 3 classes) how to write a simple program with move blocks. Then I challenged them (each class had 6 groups of 4/5 students) to program their group's robot to travel a set path through school hallways and end up back at the starting point (my classroom). They had a lot of fun, but I discovered that 2 of my motors had suddenly stopped working correctly. They moved in little jerks and barely turned at all. They had worked fine during the FLL season. After testing them with various NXT bricks and wires, I concluded that the motors were the problem. Fortunately, I had 15 total motors, and only needed 12 for the robots, so I was able to switch them out.

We got 2 of our kits from FLL the very first year of the NXT's existence. That summer, I also ordered a kit from LEGO for my personal use. The next year, we got 2 more from FLL. I have no idea which motors came from which kit, but maybe the ones from the very first year are reaching the end of their life expectancy. I have a bag of RCX motors labeled "bad bad bad" so I know those didn't last forever, either.

I bought a few more motors this summer, both to replace my bad two and to have on hand in case of another failure during the season.

Linda
Team #?